Organochlorines, including pesticides (such as DDT), are ubiquitous in the environment. All humans are exposed to low levels of these compounds. Exposure begins before birth, since the compounds cross the placenta, and continues throughout life. Evaluation of potential health effects of that exposure is essential to understanding what dangers, if any, these compounds may pose to humans. Several studies of health effects of the DDT family of compounds are underway. (1) We are studying the relationship of prenatal DDE exposure to anogenital distance (a sensitive measure of prenatal hormone exposure) in newborn boys in southern Mexico. In animals, anogenital distance is a sensitive measure of prenatal hormone exposure. DDE, the most persistent DDT metabolite, has anti-androgenic properties, and exposure to DDE reduces anogenital distance in male rats. Anogenital distance has rarely been studied in humans, so we developed a standard protocol and assessed reliability of the measurements, finding that it could be measured more reliably than other measures in current use. We are currently examining basic determinants of anogenital distance, including measures of overall body size such as birthweight. We then plan to examine the relationship of DDE to anogenital distance. (2) Our previous work had shown that DDT may adversely affect lactation, shortening the duration of lactation, although the evidence on this point is still inconclusive. We are studying this question in the same Mexican population that is being examined for anogenital distance. Followup visits to the mothers to ask about the progress of lactation are mostly completed, and preliminary data analysis has begun. (3) Previous work had shown a relationship of timing of menopause and DDE exposure. That study used postmenopausal samples to measure DDE; this is not optimal timing for measuring exposure. A new study has been done in mothers of a cohort of children we previously studied. Samples obtained from the mother around the time of childbirth were analyzed for DDE in the previous study. A questionnaire to assess menopausal status has been administered. Preliminary data analysis has begun. (4) In the menopause study, new blood samples were taken from a sample of study participants, and these have been analyzed for DDE and other organochlorines. We will compare concentrations seen in these samples with concentrations seen in the samples taken approximately twenty years earlier to assess stability of concentrations over time and examine a few potential determinants of change.